Cardiac pulse generator systems include a battery powered pulse generator and one or more leads for delivering pulses to the heart. Current pulse generators include electronic circuitry for determining the nature of an irregular rhythm, commonly referred to as arrhythmia, and for timing the delivery of a pulse for a particular purpose. The pulse generator is typically implanted into a subcutaneous pocket made in the wall of the chest. Insulated wires called leads attached to the pulse generator are routed subcutaneously from the pocket to the shoulder or neck where the leads enter a major vein, usually the subclavian vein. The leads are then routed into the site of pacing, usually a chamber of the heart. The leads are electrically connected to the pulse generators on one end and are electrically connected to the heart on the other end. Electrodes on the leads provide the electrical connection of the lead to the heart. The leads are used to sense cardiac signals from the heart and to deliver electrical discharges from the pulse generator to the heart.
The electrodes are typically arranged on a lead body in two ways or categories. A pair of electrodes which form a single electrical circuit (i.e., one electrode is positive and one electrode is negative) positioned within the heart is a bipolar arrangement. The bipolar arrangement of electrodes requires two insulated wires positioned within the lead. When one electrode is positioned in or about the heart on a lead and represents one pole and the other electrode representing the other pole is the pulse generator housing, this arrangement is known as a unipolar arrangement. The unipolar arrangement of electrodes requires one insulated wire positioned within the lead.
In general, the heart can be divided into two sides, a right side and a left side. Each side serves a specific function. The right side of the heart receives blood from the body and pumps it into the lungs to exchange gases. The left side of the heart receives the oxygenated blood from the lungs and pumps it to the brain and throughout the body.
Typically, pacing and defibrillation leads are positioned within the right chambers of the heart, or positioned within the coronary vasculature so as to position one or more electrodes adjacent a left ventricular region of the heart. From their positions within or adjacent to the ventricular chambers, the electrodes on the leads are used to sense cardiac signals and to deliver energy pulses in either a bipolar or a unipolar fashion. This sensing and pacing, however, is accomplished only within or across the chamber in which the lead is implanted. Thus, there exists a need in the art for providing additional options in sensing and delivering electrical energy pulses to a patient's heart.